Tag Archives: Tolkien

A Tolkien tide
Having been a fan of Tolkien’s faerie tales since I was chasing
squirrels in the oaks and hickories of the heartland, it’s no
surprise I’m excited to see the Hobbit. My dear Alejandra even
bought me a ticket to the opening show at our local theater. Of
course, that requires staying awake!

If you too have any intention staying up for a midnight
cinematic premier, mother nature will provide a premier low tide
(-3.6’ish) to fill the “I really should be going to bed now” hours
with “Ooo’s” and “Ahh’s” in the beam of your light. For most of the
inland Salish Sea, the tide will be in minus territory any time
after 9:pm and bottoms out around around 11:pm. It’ll probably be
wet and chilly, so dress well and feel free to share what cool
things you see through comments or by contacting me
directly.

The wrack or debris line over
this parking area indicates the peak of especially high storm tide
in early December 2012. Photo: Jeff Adams

Swollen seas
‘Tis the season for storm surges.

The week before Thanksgiving, I saw the 12’ predicted high tide
lapping on the beach as I walked off a ferry to West Seattle. A
stream babbled north under the dock, well above the tide and
buffered by large wood and another few feet of gravel/sand
beach.

I traveled the same path a week later, when the predicted high
tide was actually a few inches lower. However, the storm tide had
swamped the beach logs and stream both, lapping in the vegetation
of the recently restored shoreline. Numerous logs with cut ends had
rolled and floated out into the bay – an example of the sub-par
services cut logs provide when compared to their rooted and
branched brethren.

You may also recall the heavy rain before Thanksgiving. Along
with that came the surge that I observed and that you can see in
the graph below. The actual water levels (red) pushed almost 2 feet
higher than the predicted level (blue). The green shows the
difference between the two. When predictions hold, the green line
stays on zero.

Air pressure and predicted and
actual water levels during 2012’s pre-Thanksgiving storms.
http://tidesandcurrents.noaa.govAir pressure and predicted and
actual water levels at The Battery Station, New York City, during
Hurricane Sandy. http://tidesandcurrents.noaa.gov

Heaping on the water
Tides are predicted based primarily on the locations of the Earth,
Moon and Sun. Those astronomical or predicted tides are the numbers
we see in our tide tables, apps or calendars. We have a great deal
of certainty as to where the heavenly bodies will be at any given
time in the future, but back on our corner of the blue planet,
long-range weather details are largely unknown. Consequently, we
have no long-range ability to factor storm surges into our tidal
predictions.

Storms, caused by the collision of colder northern air and
warmer southern air, set our Pacific waters in motion. The warm air
rises, lowering the pressure the atmosphere applies to the ocean
and allowing the ocean to swell. That pressure-driven surge is
accompanied by some level of wind-driven surge, as the rising
warm air also fosters stronger winds that pile the water up on the
coastline.

Since our region is spared tropical cyclones (we seem satisfied
with earthquakes and volcanoes), our storm surges are mild compared
to what everyone watched the East Coast suffer during Hurricane
Sandy (right). Still, it’s not unusual for our waters to surge 1 or
2 feet higher than expected during stormy seas.

Our strongest storms often strike in the winter, when we also
have some of our highest predicted tides (see and be part of WA DOE’s King Tide photo
initiative). Add 20 inches of storm surge to an already high
tide, then throw in some high wind and waves… repairs to shoreline
properties, roads, and utilities often follow. Factor in potential
effects of climate change (a few inches of sea level rise, more
intense storms), and the issue of storm surge becomes an important
consideration with regards to shoreline infrastructure. Oh, and
that kayak that you didn’t bother to tie up because it was 2
vertical feet above the highest predicted tide… (ouch!)

Tide fun courtesy of NOAA
If you enjoy exploring graphs and numbers, you can have some fun
through NOAA’s Tides & Currents portal. You can even check
out sea level changes over time and historical extremes. The
“Seattle, Puget Sound” station’s highest recorded water level was
in January 1983 at +14.48 (right). Not too bad considering our
recent big surges were about +14. Certainly nothing compared to the
extra 10 feet piled onto the east coast shorelines.

When you’re playing with the numbers and graphs, remember the
-8hr conversion from GMT and a -7.94 feet conversion from the
extremes section to make them comparable to what we’re used to
seeing (based on mean lower low water [MLLW] as 0.0, instead of the
station standard that’s 7.94 feet below MLLW).

Have fun exploring NOAA’s online tidal treasures and our last
lowest tide of the year! And if you fall asleep at work or school
tomorrow… you didn’t read this.